A printed circuit board (PCB) mechanically supports and electrically connects various electronic components and connectors using conductive traces, pads and other features etched from, for example, copper sheets laminated onto a non-conductive substrate of a dielectric material. PCB's can be single sided (one copper layer), double sided (two copper layers) or multi-layer. Multi-layer PCB's may typically use multiple cores that include two patterned conductive layers and a central dielectric layer that are laminated together forming a composite structure. The conductors on different layers are electrically connected with vias. There are several types of vias utilized in traditional PCB design, such as, plated through holes (PTH), buried vias, and blind vias, which are standard for PCB design. A PTH utilizes a drilled hole extending through the composite structure and is typically plated with a conductor, such as copper, providing electrical continuity between the various conductive elements of a circuit.
High speed circuit boards traditionally utilize multi-layer structures that include ground planes, voltage planes and transmission lines that can be interconnected between layers by electrically conductive vias. While necessary in multi-layer PCB's to connect the various signal lines and planes in different PCB layers, vias can be discontinuities for high speed signal transmission causing signal reflections and degradation of the signal integrity. Portions of a conductive via extending beyond the interconnected inner layers of the PCB can form an unterminated via stub. The presence of these unterminated stubs in high speed circuits can act to produce undesirable signal reflections leading to signal degradation. Back drilling is a process used to remove most of the unwanted stubs by mechanically drilling the unused portion of the PTH to a certain depth with a larger diameter hole. The process of back drilling increases the manufacturing cost to produce the PCB as a result of the additional process steps and possible reduced yield. In addition, the via is no longer electrically accessible with test equipment after the backdrilling process.